One corrosion resistant metal alloy coating that is used widely in Australia and elsewhere for building products, particularly profiled wall and roofing sheets, is an Al—Zn alloy coating, more particularly a coating formed from a 55% Al—Zn alloy that also comprises Si in the alloy. The profiled sheets are usually manufactured by cold forming painted, metal alloy coated strip. Typically, the profiled sheets are manufactured by roll-forming the painted strip.
The addition of Mg to this known 55% Al—Zn alloy has been proposed in the patent literature for a number of years, see for example U.S. Pat. No. 6,635,359 in the name of Nippon Steel Corporation.
It has been established that when Mg is included in a 55% Al—Zn alloy coating, Mg brings about certain beneficial effects on product performance, such as improved cut-edge protection.
The applicant has carried out extensive research and development work in relation to Al—Zn—Si—Mg alloy coatings on strip such as steel strip. The present invention is the result of part of this research and development work.
The above discussion is not to be taken as an admission of the common general knowledge in Australia and elsewhere.